RESULTS
The search strategy retrieved 3281 articles from databases that were imported to EndNote Web. A total of 576 studies were duplicates. After these were excluded, two independent authors screened the remaining 2705 titles, 193 of which were assessed for eligibility using the abstract. A total of 187 studies were excluded due to inappropriate study design, population, inappropriate intervention, or lack of outcome data. After full-text analysis, six studies met the inclusion criteria, five of which could be combined in the meta-analysis. The PRISMA flow diagram summarizes the study selection process (Figure 1). The characteristics of the included studies are shown in Table 2.